As an electrolyte membrane for a polymer electrolyte fuel cell (PEFC) (or proton exchange membrane fuel cell (PEM-FC)), a perfluorosulfonic acid membrane typified by Nafion (trade name) membrane of E. I. du Pont de Nemours and Company is generally used. However, this membrane has disadvantages such that the proton conductivity is still low; the power generation efficiency is low because a fuel is liable to permeate when a liquid fuel such as alcohol or the like is used; and the change in dimension thereof at the time of swelling is large.
Therefore, an electrolyte membrane in which a proton conductive component is infiltrated in pores of an insulating porous film has been studied. The electrolyte membrane having such a structure can suppress alcoholic permeability and reduce dimensional changes due to containing water while maintaining the electrical conductivity by using an insulating porous film for a base material.
Japanese Patent Application Laid-Open No. 2004-146279 discloses an electrolyte membrane obtained by infiltrating the inside of a porous base material with a monomer and polymerizing the monomer, and refers to 2-methylpropane-2-acrylamide sulfonic acid as the monomer and to polyimide and polyolefine as the porous base material.
However, according to the technology disclosed in Japanese Patent Application Laid-Open No. 2004-146279, since the adhesion of the porous base material and the infiltrating component is insufficient, it is considered that the polymer drops out from the inside of the pores during use for a long period of time, resulting in lowering of the output (the durability is insufficient).
Further, Japanese Patent Application Laid-Open No. 2000-277131 discloses an electrolyte membrane composed of an ion exchanger obtained by copolymerizing a lipophilic monomer, a heterocyclic monomer, a carboxylic acid-based monomer, and a strong acid group-based monomer, and an electrolyte membrane formed of a porous film. A morpholine ring is mentioned as the heterocyclic monomer, and polyimide is mentioned as the porous film.
However, according to the technology disclosed in Japanese Patent Application Laid-Open No. 2000-277131, even if the polyimide porous film and the ion exchanger containing the morpholine ring are adhered to each other by the interaction of a functional group, it is considered that the adhesion therebetween is insufficient, and therefore the durability is insufficient.
According to the present invention, an electrolyte membrane with high adhesion between a porous film and a proton conductive component can be obtained. Further, by using the electrolyte membrane, a fuel cell with high durability can be provided.